linux-kernel - Re: [PATCH 3/4] selftests/sgx: Harden test enclave API

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Message-ID: <a1bd8864-a7df-9fc8-8257-bfc0d3620c22@cs.kuleuven.be>
Date:   Thu, 20 Jul 2023 21:34:20 +0200
From:   Jo Van Bulck <jo.vanbulck@...kuleuven.be>
To:     Jarkko Sakkinen <jarkko@...nel.org>, linux-sgx@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     dave.hansen@...ux.intel.com
Subject: Re: [PATCH 3/4] selftests/sgx: Harden test enclave API

On 20.07.23 19:32, Jarkko Sakkinen wrote:

>> +#define PANIC()								\
>> +	asm("ud2\n\t")
> 
> any reason not to use static inline function?
>

Thanks for the suggestion, no reason in this case. Apart perhaps that 
it's only 1 line of code and an inline function may seem a bit like a 
waste (given that gcc does not inline until certain optimization 
levels). I can surely change it to static inline void panic(void) if you 
prefer?

>> +#define SAFE_COPY_STRUCT(u_arg, t_cp)					\ >> +	do {								\
>> +		/* 1. check if the argument lies entirely outside */	\
>> +		if (!is_outside_enclave((void *)u_arg, sizeof(*t_cp)))	\
>> +			PANIC();					\
>> +		/* 2. copy the argument inside to prevent TOCTOU */	\
>> +		memcpy(t_cp, u_arg, sizeof(*t_cp));			\
>> +	} while (0)
>> +

This could be made into a static inline function, but then t_cp would 
have to be type void* and sizeof(*t_cp) won't work anymore and a third 
parameter to pass the sizeof would be needed, which would require the 
caller to pass it correctly. Hence, a macro seems "safer" to me here in 
this instance as it requires only 2 arguments. Agreed?

>> +#define ASSERT_INSIDE_ENCLAVE(u_arg, size)				\
>> +	do {								\
>> +		if (!is_inside_enclave(((void *)(u_arg)), size))	\
>> +			PANIC();					\
>> +	} while (0)

This macro could certainly be turned into a static inline void function 
if preferred.

Best,
Jo